Known in the art is a spark ignition type internal combustion engine which is provided with a variable compression ratio mechanism which can change the mechanical compression ratio and a variable valve timing mechanism which can control a closing timing of an intake valve and which is designed to maintain an actual compression ratio substantially constant regardless of an engine load (see, for example, Patent Literature 1). In this internal combustion engine, as the engine load becomes higher, that is, as the demanded intake air amount becomes greater, the closing timing of the intake valve is advanced to approach intake bottom dead center. At this time, to maintain the actual compression ratio substantially constant, the mechanical compression ratio is made to drop as the demanded intake air amount becomes greater.